As a flexible heating soft floor mat using a heating fluid such as warm water, etc., as heating medium, there is generally known a structure that conduits for passing a heating medium are meanderingly disposed on base sheet which forms a heat insulating layer for mat and a cover material is placed on the surface side thereof. Also, as the material for the base sheet, expanded polyurethane (see Japanese Laid-Open Utility Model Application No. 96515/85), sponge (see Japanese Laid-Open Utility Model Application No. 146215/85), or a polyethylene uncrosslinked foamed article (see Japanese Laid-Open Utility Model Application No. 60608/85) is used.
Also, as the material for conduits, a heat resistant rubber (see Japanese Laid-Open Utility Model Application No. 146215/85) or a synthetic resin such as polyvinyl chloride and polyethylene (see Japanese Laid-Open Utility Model Application No. 96515/85) is used. Furthermore, it is known to use crosslinked polyethylene (see, e.g., Japanese Laid-Open Utility Model Application No. 116714/84).
However, in the case of using the conventional base sheet on which conduits are disposed, there are such problems that the base sheet is greatly deformed at use due to the poor heat resistance thereof, an attempt of imparting heat resistance to the material reduces the flexibility to reduce the adaptability to floor and feeling thereof, and also the material for the base sheet has a high heat transferability due to the continuous cells thereof, which results in causing large heat loss.
Also, when conduits are composed of a rubber or polyvinyl chloride, there are problems of reducing the heat aging resistance and the pressure resistance thereof by the action of heating medium. On the other hand, conduits composed of ordinary polyethylene (density of from 0.910 to 0.925 g/cm.sup.3) are insufficient in flexibility, which inevitably gives trouble for keeping the flexibility (e.g., rolling up property of mat) of heating floor mat. Thus, means for solving these problems have been desired.
Furthermore, in the case of using conduits composed of crosslinked polyethylene having high rigidity, there are such problems that when conduits extend by causing heat expansion at passage of heating medium, the heat expansion force is concentrated to curved portions of the conduit meanderingly disposed, with it being transferred and hence the conduit is expanded at the curved portions to rise and abnormally deform the mat, whereby the mat gives feeling of incongruity and poor habitability at use.